Several techniques for communicating power and data over a single bus are known in the art. A well-known example is “Power Line Communication” (PLC) where data is carried on electrical conductors that are simultaneously used for carrying AC electrical power. A specific example is “Homeplug”, which is the family name for various power line communication specifications that support networking over existing home electricity wiring. Characteristic to such systems is that the power is a low-frequency AC signal (e.g. 220 V at 50 Hz), and that the data-information is super-imposed at the transmitter side as a high-frequency signal (e.g. up to 30 MHz), which data-signal can be separated from the power-signal by appropriate filter-techniques at the receiver side. A disadvantage of such a system is that it requires a modem at each transmitter and receiver side, which makes this system prohibitively expensive for some applications, and requires extra board space (as compared to systems not requiring a modem). Another disadvantage is that the devices connected to the bus are galvanically coupled to the bus, unless a transformer is used, which again makes the slave units, and thus the system bulky and expensive.
FR2612019A1 discloses a system including a two-line bus, e.g. a shielded twisted pair, and several units connected to the bus. The bus is equipped with a general supply transformer, and each unit of the system is coupled to the bus by a first transformer. Each unit is also coupled to the bus by an isolating transformer with ferrite core, intended for transferring digital signals between bus and unit. A disadvantage of such a system is that each unit requires a first transformer for receiving power, and an isolating transformer with a ferrite core for the data-communication. That makes the units, and thus the system bulky, heavy and expensive.
WO2011/036147 describes a system for balancing charge over a plurality of rechargeable energy storage devices 12, e.g. battery cells, coupled in series, as illustrated in FIG. 1. The slave devices (here: balancing units 15) are galvanically separated from the power-bus 30 by means of series capacitors 19. The data communication between the slaves and the main control unit 20 occurs on a separate bus 40, e.g. a CAN bus. As the slaves 15 are at different potentials, they cannot be connected directly to the CAN-bus, but e.g. may be connected thereto by means of interface devices using opto-coupling, which requires board space and increases the component cost.
FIG. 1 shows a system 13 for recharging a plurality of battery cells 12, connected in series to form a string 11, each cell 12 being controlled by a balancing unit 15. The main control unit 20 of this system comprises an AC signal generator 14 for providing power pulses on the bus 30, which are provided to the slave units 15 through series capacitors 19. A portion of that power is used for the local power supply 22 of the slave unit, see FIG. 2, for powering a local micro-controller 18. The micro-controller 18 is arranged for opening and/or closing switches SW1, SW2 for charging and/or discharging the corresponding battery cell 12. Another portion of the power pulse is used for charging or discharging the corresponding battery cell 12. The micro-controller 18 can measure e.g. the voltage of the battery cell 12 by measuring the voltage difference over the pins S+ and S− by means of an internal A/D convertor 21. Via a second bus 40, separate from the power bus 30, the main control unit 20 can send commands to each of the slave units 15, e.g. to instruct a particular slave unit to measure the cell voltage of the corresponding battery cell 12, and when the value is measured and digitized by means of an A/D convertor 21, this particular slave unit can send the measured voltage value via the data bus 40 to the main control unit 20. The interested reader is kindly referred to EP2302757A1 for more details.
The second bus 40 can e.g. be a (well known) CAN bus. However, as the slave units 15 are connected to the storage elements 12, which are connected in series, the slaves 15 are at different potentials, and therefore they cannot be connected directly to the second bus 40, but need to be connected via galvanic separation means, such as e.g. opto-coupling.
FIG. 2 shows one of the balancing units 15 of the rechargeable energy storage system of FIG. 1 in more detail. As the control and purpose of the switches SW1 and SW2 is described in EP2302757A1. Node “P”, is where power is injected from the power bus 30 via the series capacitor 19, and the node “C” is the node through which the micro-controller 18 and the main control unit 20 can communicate via the second bus 40. The communication interface is not described in detail in EP2302757A1.
There is a need for another method and system for providing power and data on a bus.